Electro-thermal transducer



May 5, 1970 R. E. BOWLES ELECTED-THERMAL TRANSDUCER Filed July 7, 1964 0 WBM E.

2 m w 6 m w 1 w. a M P w p MM m ATTORNEYS United States Patent 3,509,896 ELECTRO-THERMAL TRANSDUCER Romald E. Bowles, Silver Spring, Md., assignor to Bowles Engineering Corporation, Silver Spring, Md., a corporation of Maryland Filed July 7, 1964, Ser. No. 380,816 Int. Cl. Fc 1/08 US. Cl. 13781.5 18 Claims ABSTRACT OF THE DISCLOSURE An analog fluidic amplifier includes a power nozzle for issuing a power stream of fluid, a pair of receivers for receiving the power stream and heat applying means for heating and increasing the specific volume of a portion of the fluid in the boundary layer of the power stream to cause the stream to be proportioned to one or another of the receivers as a function of the applied heat.

related in their utility in certain cases, it has become desirable to provide an electro-fluid transducer that is highly efficient and maintenance free. Accordingly, it is proposed in the present invention to provide a proportional fluid amplifier with electrical control having no moving parts.

In prior art devices, electro-fluid systems have utilized moving parts for effecting changes in fluid flow, such as electrically operated valves to control the flow of fluid in the control jets of pure fluid systems. These systems thus contain moving parts hich are undesirable in the ense of speed, reliability and maintenance.

It has been proposed to ionize a gas in a fluid amplifier and control the stream flow by establishing an electrical field acros the stream. However, this system has proved to be generally limited in its application since very high electrical voltages are required which are dangerous and which do not lend themselves to most applications.

It has also been proposed to produce a high-intensity heat shock in a digital fluid amplifier to effect switching of the direction of the fluid stream. While this type of action is acceptable in a flip-flop device, it is totally unacceptable for the analog amplifier. More particularly, a heat-generated shock wave is discontinuous in nature and thus is not generally susceptible for use in analog systems.

The present invention is concerned with providing electrothermal control of fluid amplifiers by means of control of thermal expansion of fluid in a central location of a fluid amplifier. The invention may be employed in both of the well-recognized types of analog or proportional fluid amplifiers; that is, the momentum exchange and the boundary layer control types of amplifiers.

In the momentum exchange type of fluid amplifier, a nozzle directs a power stream toward a receiving duct system in accordance with signals provided by a system of relatively low energy control streams. The control streams are directed against the sides of the high velocity regions of said power stream. The power stream is de- 3,509,896 Patented May 5, 1970 flected in accordance with the amount of momentum exchanged between the control streams and the power stream and is variably proportioned between the receiving ducts. Thus, it is possible to direct a high energy stream to a receiving duct system in a controlled manner using lower energy control streams. This constitutes fluid amplification of the control stream signal and thus the name, fluid amplifier.

In the boundary layer control type of analog or proportional amplifier, the control function is achieved by controlling flow of fluid into and out of a boundary layer region of the power stream so as to control the difference in static pressure across the stream. This type of device depends upon a change in one of the fluid parameters in a localized region of the boundary layer region. For example, the specific volume, thermal energy level, mass transport properties or pressure of the fluid in the boundary layer regions of the amplifier can be varied so as to cause a deflection of the power stream and a proportioning of the power stream between the receiving ducts.

In the first embodiment of my invention, an analog amplifier which may exhibit characteristics of both the momentum exchange and the boundary layer types of amplifiers has control passages with control nozzles which are adapted to issue low energy fluid control streams into the interaction region of the amplifier. The total momentum of these control streams is controlled by a heater acting on a constant mass flow of fluid passing through the control passages. In this embodiment, the fluid first passes through a metering throat, is heated by any suitable means to increase the specific volume and is expanded by the control nOZZle just before it meets with the boundary layer of the power stream in the interaction region of the amplifier.

In this first type of fluid amplifier, there are at least three different methods or modes of operation to be considered when a compressible fluid is being used. One of these modes has to do with supersonic flow of the control streams and the other two modes have to do with subsonic flow. When an incompressible fluid, such as water at normal pressures, is used still another mode of operation takes place. According to the second embodiment of the present nvention, an analog amplifier of the boundary layer type is provided with thermal controls. The control of the power stream depends on the change in specific volume of the fluid in a localized area of the boundary layer region. Heater elements for expanding the fluid are placed just downstream of the orifice of the power nozzle in the boundary layer regions between the power stream and the sidewalls of the amplifier. A limitless source of fluid is provided for the boundary layer region so that fluid will always be available for expansion. This source of fluid may come from a downstream recirculation in the boundary layer or, in the alternative, a low level supply from a supply nozzle in the heating area. As the heater elements are actuated, the change in the fluid specific Volume caused by the fluid thermal expansion in these localized areas of the boundary layer region causes an effective increase in fluid volume and effective pressure i.e., an outward expansion from the amplifier sidewall so that a deflection of the power stream in the transverse direction necessarily results. The power stream is proportioned to the plural receiving ducts in accordance with the signal provided by the thermal controls in this manner.

In both the first and second types of systems outlined above, either a compressible or an incompressible fluid may be used as the working medium. When an incompressible fluid such as a liquid is used, an additional amplification may be obtained by relying on change in phase from liquid to gas. In any case, the response is smooth and continuous, particularly adapted for analog operation.

Broadly, therefore, it is an object of this invention to provide an electro-thermal fluid analog device.

It is another object of this invention to provide an analog fluid amplifier with highly sensitive, electrically initiated, thermal control signals.

Still a further object of this invention is to provide an analog fluid amplifier that relies on a thermally actuated change in the volumetric flow rate or the specific volume of the fluid for the control signal.

It is yet another object of this invention to produce a thermally actuated analog fluid amplifier control signal from a constant mass flow control stream.

The above and still further objects, features and advantages of the present invention will become apparent upon consideration of the following detailed description of several embodiments thereof, especially when taken in conjunction with the accompanying drawings, wherein:

FIG. 1 is a schematic diagram of an analog fluid amplifier type according to the present invention, wherein the momentum or the volumetric flow rate of fluid into the boundary layer region is utilized for a control signal;

FIG. 2 is a plan view of one-half of the fluid amplifier of FIG. 1, the other half of the amplifier being a mirror image;

FIG. 3 illustrates a graph showing the specific volume change of water for constant heat addition rates, wherein it can be seen that a change in phase will take place at a low pressure;

FIG. 4 is a plan view illustrating one-half of an analog amplifier of the boundary layer type according to the present invention, wherein fluid volume change is utilized for a control signal, the other half of the amplifier being a mirror image; and

FIG. 5 is a modification of the embodiment illustrated in FIG. 4, wherein additional fluid is supplied to the heating area of the boundary layer region.

According to the embodiment of the invention illustrated FIGS. 1 and 2 of the accompanying drawings, an analog proportional fluid amplifier 11 is provided having fluid passages 12, 13 terminating in control nozzles 14 and 15, respectively, adapted to issue control streams. A fluid power source 16 supplies the fluid to the passages 12, 13 as well as to amplifier power nozzle 17, which is adapted to issue a power stream.

The power stream is issued from the nozzle 17 of the amplifier toward receiving ducts 21, 22, which are directed toward said nozzle at an angle with respect to the amplifier centerline, as illustrated in the drawings. The amplifier 11 may be provided with a center channel 23 to receive fluid directed along the centerline of the amplifier thereby reducing the amount of fluid that must be accepted by the receiving ducts 21, 22 except when the power stream is fully deflected. Said channel 23 can merely dump" the fluid delivered thereto by returning it to a sump or venting it to atmosphere or can be itself used to provide a signal. Itis to be understood that this center channel is optional and a conventional center divider could be employed.

The momentum of the control streams determines the direction of the power stream as it issues from the interaction region, which is just downstream of the orifice of the power nozzle. The enlarged regions 24, which communicate with the interaction region are employed as equal pressure fluid reservoirs to maintain the static pressures along the power stream downstream of the control nozzles at a fixed value and thus limit deflection of the power stream as a result of boundary layer effects. Since there is no solid boundary adjacent the power stream in the interaction region of the amplifier, the tendency for power-stream-sensitive, troublesome, low-pressure regions to form in the boundary layer is eliminated. This is true since any fluid that is removed by entrainment is immediately replaced by fluid from the reservoir of fluid in the enlarged regions 24. Apertures 25 are employed to connect the enlarged regions to the sump or to the atmosphere which is a limitless source of or sump for fluid.

Under any condition when the signal to the amplifier from control passages 12, 13 is balanced, the main flow of fluid is directed toward the center channel 23. The flow to receiving ducts 21, 22 at this condition is a relatively small amount, and the flow is symmetrical, i.e. the amount of fluid entering duct 21 is equal to the amount entering duct 22. When the flow to ducts 21, 22 is symmetrical, a null condition exists and no dilferential output signal is present. It is when the input signals from control passages 12 and 13 are unbalanced that a null condition no longer exists and greater or lesser amount of fluid flows to one or the other of the receiving ducts 21, 22 creating an amplified, unbalanced condition or output signal. This output signal is used for the desired control function.

According to this embodiment of the invention, the input signals to the analog amplifier 11 are provided by control passages 12, 13 which have been referred to above. The operation of these passages will be explained below with reference to FIGS. 1 and 2. It is pointed out that, since the input signal that controls the analog amplifier is an electro-thermo signal, these control passages, in conjunction with a heater element, act as electro-fluid transducers, which feature is an important aspect of this invention.

Taking control passage 12 as exemplary, the passage 13 being a mirror image and therefore not being discussed, fluid is supplied to the passage at inlet 30. The fluid is passed through restrictor orifice 31 and throat 32 of the nozzle 14 so that the pressure in the respectively remaining portions of the passage 12 is reduced and so that the flow through the control nozzle 14 may be isolated from pressure variations which might occur downstream of nozzle 14. Orifice 31 and throat 32 also serve to maintain a constant mass flow rate in the passage 12 while throat 32, in addition, inhibits feedback from the region downstream thereof which is very important, as will be seen later.

As the fluid is expanding downstream of the throat 32, the fluid enters a heating region, in a divergent portion of nozzle 14 generally represented 'by numeral 33 in the drawings. A suitable heater 34 is employed in this region 33 to heat the fluid as desired. A coil of wire is illustrated for this purpose in FIG. 1. The heater is preferably attached to the side of the passage or embedded in the wall so that fluid flow will not be impeded. Any suitable metal wire may be employed for the heating element, such as platinum, copper, etc. It is also to be understood that suitable electrodes, placed at opposite sides of the passage at region 33, as illustrated in FIG. 2, may be employed to heat the fluid by current flow through the fluid, which in this case must be conductive. Also, it is to be understood that any suitable heat exchanger can be employed in lieu of the electrical heater.

As indicated above, there are a number of different methods or modes of operation of the present invention illustrated in FIGS. 1 and 2. When using a compressible fluid, such as air, there are basically three modes of operation. In one of these modes, the flow in the nozzle 14 is supersonic and such operation has been found to produce essentially momentum exchange type of amplifier. In the other two modes, the flow issuing from said nozzle 14 is subsonic, and the amplifier exhibits some characteristics of a boundary layer type of amplifier.

In the first two modes to be discussed, the flow at the throat 32 of the nozzle 14 is sonic or Mach I. By controlling the pressure downstream of the throat 32 when the flow generated by said throat is at Mach I, the control stream issuing from nozzle 14 can be made to be either supersonic or subsonic flow. It is pointed out that the flow at the throat 32 can never exceed Mach I due to the formation of a shock wave when supersonic flow is approached.

In the first mode of operation to be considered, the compressible fluid flow at the throat 32 is at Mach I and with the proper design of the divergence of the nozzle 14, the within nozzle effects of static pressure acting at the exit of said nozzle 14 is negligible and the flow at the exit of the nozzle 14 is supersonic. In this case, upon the addition of heat at point 33, the specific volume of control fluid is increased due to thermal expansion, which is converted into kinetic energy and a corresponding momentum by expansion at divergent nozzle 14 deflecting the power stream accordingly. This mode is essentially a momentum exchange operation since the fluid flow is supersonic. The momentum involved here consists essentially of the dynamic momentum or m'V Where m is the fixed mass flow rate of the fluid and V is the velocity, at the exit of nozzle 14.

In the second mode of operation, the flow generated by the throat 32 is stil at Mach 1, but due to over expansion of the nozzle 14, the nozzle exit pressure causes a normal shock within the nozzle which effects the exit momentum of the control nozle. Thus, in this case, there is an added momentum factor dependent upon the location of the normal shock and the fluid thermal energy. The total momentum of the stream entering the boundary layer region and acting to deflect the power stream in this case then, is varied in accordance with variations of the heat energy added to the stream at region 33.

This second mode is basically a combination momentum exchange and boundary layer type operation since the flow at the exit of nozzle 14 is subsonic; however, it is difficult in any system to determine the relative effect of the momentum factor and the pressure factor of the increase in heat energy. Suflice it to say that, in a hybrid operation such as in this mode, which factor increases and how much depends on many design factors in the device and that it is unimportant here for present purposes to determine which factor is affected the most.

In either of these first two modes of operation, that is, where the flow at the throat 32 is Mach I, the control fluid in passage 12 in the region upstream of the orifice 32 is completely unaffected by any pressure fluctuations downstream, since such fluctuations are limited by the throats Mach I velocity and thus cannot travel upstream. As previously indicated, this is a very important feature of the present invention because when pressure fluctuations are eliminated in passage 12 upstream of the orifice 32, the mass flow rate is maintained constant within very close limits independent of the electro-thermal control signal. Also, the thermal energy is converted into useful energy at the nozzle 14. Consequently, the deflection of the power stream may be precisely controlled in accordance with the thermal energy added for a very accurate analog control function.

A third mode of operation of the device shown in FIGS. 1 and 2 is when the fluid flow through the throat 32 is subsonic. In this case, the pressure fluctuations downstream of said orifice are not completely isolated from the upstream region of passage 12, but the orifice does inhibit feedback to an appreciable degree. In this case, when heat energy is added to the control fluid as before, the total momentum and the volumetric flow rate out of the exit of nozzle 14 will be increased. In this case, the pressure factor of the total momentum equation is the controlling factor although some increase in the kinetic energy term is produced by an increase in heat energy.

At this point, it is well to point out the operation of the device of FIGS. 1 and 2 is as set forth above when a compressible fluid is used as the Working medium. The operation of the system of FIGS. 1 and 2 is quite different when an initially incompressible fluid is employed. The term incompressible is meant in terms of pressure not in terms of temperature; that is, the fluid must exhibit a significant volumetric change with a change in temperature but not with anticipated change in pressure. Water at normal pressures is a case in point.

Referring again to FIG. 2, water is heated in region 33; it expands and increases in specific volue with a corresponding increase in the volumetric flow rate toward the exit of nozzle 14. By controlling the heat added and thus the flow rate of the control streams into the boundary layer regions of the power stream, very sensitive control of the pressure across said stream is obtained.

When using a liquid such as water as the working medium, a very important advantage is realized in the present invention. This advantage airises from the fact that it is possible to use a change in phase or partial change in phase of the control fluid in this case to achieve an increase of specific volume. This is important since, in a boundary layer unit, the amplification is enhanced if the specific volume of the control fluid being introduced into the boundary layer regions is considerably greater than the fluid of the power stream. An obvious example of the foregoing phenomenon is a power stream of water being controlled by control streams of air. In the present invention, the formation of steam in the boundary layer control region when a sufficient amount of heat is applied greatly enhances the amplification.

The rate of change in specific volume of water for constant heat addition rates within a range of pressures is shown in FIG. 3. It is noted that, at low pressures, the change in specific volume increases rapidly for a given application of heat due to a change of phase from liquid to gas and a corresponding rapid increase in volumetric flow rate in nozzle 14 is realized. This increase in the volumetric flow rate is a smooth and continuous operation, especially adapted for analog amplification, since the curve is continuously variable rather than linear for a given application of heat.

A schematic diagram of an electrical circuit to control the heater 34 is shown in FIG. 2. Electrical power is supplied from any suitable power source 35 which may be controlled by a rheostat 36 and a signal source 37. By carefully controlling the rheostat and the actuation of the signal source, a highly sensitive analog control action may be obtained.

A second embodiment of my invention is illustrated in FIG. 4, wherein like numbers represent like elements as illustrated in FIG. 2. Analog amplifier 11a, which is of the boundary layer type, depends upon a change in condition of the fluid in a localized area of the boundary region for control. Therefore, in this embodiment, heating region 33a is located at an L-shaped portion of the sidewall just downstream of power nozzle 17 and in the boundary layer of the power stream. Heater 34a can be either a coil as illustrated or suitable electrodes with conductive fluid.

As in the case of the analog amplifier 11 of the first embodiment of my invention, enlarged regions 24 are provided to limit boundary layer lock-on eflects, i.e., an excessive degree of boundary layer positive feedback. Said regions 24 also furnish a supply of fluid in the heating region 23a ready for expansion upon heating. Since the heating region 33a in this embodiment is bounded by an L-shaped wall of the amplifier, when thermal expansion and change of mass transport properties takes place upon actuation of the heating coil 34a, a resulting change in static pressure across the power stream deflects it. Also, a tendency for an increase in pressure at 33a will be directed outwardly from the amplifier wall against the high velocity regions of the power stream. This outward pushing caused by thermal expansion of the fluid helps deflect the power stream towards the right, as viewed in FIG. 4. The deflection causes a change in the proportioning of the fi-uid to the receiving duets, with duct 22 receiving the lesser amount.

In a modification of the device of FIG. 4 shown in FIG. 5, a boundary layer unit is provided with a supply passage 40, which supplies fluid at a low level of energy to the heating region 33]) via orifice 41. The heating coil 34b extends along the L-shaped wall of the heating region 33b, through orifice 41, and into the passage 40, so that a maximum amount of fluid contacts said coil. This fluid assures that the L-shaped heating region 33b is at all times supplied with a maximum amount of fluid to be expanded for control purposes. It is pointed out that this additional fluid is supplied only to prevent starvation of the heating region 33b and that, although acting as a bias signal, it provides no variable control functions as such.

As in the boundary layer units of FIGS. 1 and 2, a very nice result is obtained from using an initially incompressible fluid, such as water, as the working medium in the embodiment of FIGS. 4 and 5. Above the critical pressure, no change in phase will occur, the deflection of the power stream being solely a result of the thermal expansion of the water. However, below the critical pressure, a very rapid change in specific volume can occur denoting a change of phase for all or a portion of the control fluid for a given application of heat (see FIG. 3). By using heat addition rates to cause a change in phase, a greater sensitivity may be imparted to the system, as was pointed out above, since the vaporized control fluid is of a much greater specific volume than the power stream which it is controlling.

While I have described and illustrated several specific embodiments of my invention. it wall be clear that variations of the details of construction which are specifically illustrated and described may be resorted to without departing from the true spirit and scope of the invention as defined in the appended claims.

What I claim is:

1. An analog fluid amplifier device comprising a power nozzle adapted to issue a power stream of fluid, plural receiving means directed toward said power nozzle for receiving said stream, and heat applying means located proximate said power nozzle in the boundary region of said power stream for heating and increasing the specific volume of a portion of the fluid in the boundary layer region of said power stream to cause said power stream to be proportioned to one or another of said receiving means in proportion to the amount of heat applied.

2. The analog fluid amplifier device of claim 1 wherein is provided fluid supply means for issuing fluid into said boundary layer region adjacent said heat applying means.

3. The analog fluid amplifier device of claim 2 wherein said fluid supply means comprises a fluid passage terminating in an orifice for issuing said fluid, said heat applying means being a coil of wire with a portion thereof extending through said orifice and into said passage and another portion thereof extending into said boundary layer region.

4. The analog fluid amplifier device of claim 1, wherein said fluid is conductive and said heat applying means comprises spaced plural electrodes in said boundary layer region adapted to be electrically energized to heat the fluid by current flow through said fluid and electrical power means to energize said electrodes.

5. The analog fluid amplifier of claim 1 wherein the fluid of said power stream is substantially incompressible.

6. The analog fluid amplifier of claim '5 wherein said power stream fluid is water, and the heating range of said heat applying means is such as to cause said fluid in said boundary layer portion to change from liquid to vapor.

7. An analog fluid amplifier device comprising a power nozzle adapted to issue a power stream, a control nozzle for issuing a control stream directed against said power stream, plural receiving means directed toward said power nozzle for receiving said power stream, and heat applying means at said control nozzle for heating and increasing the energy of the control stream in passing through said control nozzle to thereby cause said power stream to be proportioned to one or another of said receiving means in proportion to the amount of heat applied, wherein a portion of said control nozzle in the region of said heat applying means is divergent in a downstream direction to convert said energy into momentum, the throat of said nozzle being upstream of said divergent portion thereby maintaining constant mass flow and inhibit ing feed back of said control stream.

8. An analog fluid amplifier device comprising a power nozzle adapted to issue a power stream, a control nozzle adapted to issue a. control stream directed into the boundary layer region of said power stream and plural receiving means directed toward said power nozzle for receiving said power stream, said control nozzle comprising pressure reducing means, and heater means downstream of said pressure reducing means for heating and increasing the volumetric flow rate of said control stream, said control nozzle being divergent in a downstream direction in the region of said heater means for increasing the momentum of said control stream toward said power stream to cause said power stream to be proportioned to one or another of said receiving means in proportion to the amount of heat applied.

9. The analog fluid amplifier device of claim 8, wherein said fluid is conductive and said heater means comprises spaced plural electrodes in said control stream adapted to be electrically energized to heat the fluid by current flow therough said fluid and electrical power means to energize said electrodes.

10. The analog fluid amplifier device of claim 8, wherein said heater means comprises a coil of wire adapted to be electrically heated and electrical power means to heat said coil.

11. The analog fluid amplifier of claim 8 wherein said fluid is substantially incompressible.

12. An analog fluid amplifier comprising a power nozzle adapted to issue a power stream, control nozzle means having a throat and a divergent portion and being adapted to issue a control stream directed against saidpower stream at a constant mass flow rate, plural receiving means directed toward said power nozzle for receiving said power stream, and heater means in said divergent portion of said control nozzle for heating and increasing momentum of said control stream to cause said power stream to be proportioned to one or another of said receiving means in proportion to the amount of heat applied.

13. An analog fluid amplifier device comprising a power nozzle adapted to issue a power stream, a control passage means terminating in a control nozzle having a divergent portion adapted to issue a control stream into the boundary layer region of said power stream, plural receiving means directed toward said power nozzle for receiving said power stream, and heater means in said divergent portion of said control nozzle for heating and increasing the heat energy of the control stream to thereby cause said power stream to be proportioned to one or another of said receiving means in proportion to the amount of heat applied.

14. The analog fluid amplifier device of claim 13 wherein said control nozzle further comprises restrictor throat means upstream of said divergent portion for generating Mach I flow of said control stream, said divergent portion converting said heat energy to momentum with the flow of said control stream at the exit of said portion being supersonic, said control stream thereby effecting said p'roportioning of said control stream by essentially momentum exchange operation.

15. The analog fluid amplifier device of claim 13 wherein said control nozzle further comprises restrictor throat means upstream of said divergent portion for generating Mach I flow of said control stream, said divergent portion converting said heat energy to momentum with the flow of said control stream at the exit of said portion being subsonic, said control stream thereby effecting said proportioning of said control stream by essentially boundary layer operation.

16. The analog fluid amplifier device of claim 13, wherein said control nozzle further comprises restrictor throat means upstream of said divergent portion for generating subsonic flow of said control stream, said divergent portion converting said heat energy to momentum with the flow of said control stream at the exit of said portion being subsonic, said control stream thereby effecting said proportioning of said control stream by essentially boundary layer operation.

17. An analog fluid amplifier, comprising:

a source of pressurized fluid;

a power nozzle connected to said source for issuing a power stream of said fluid;

plural receiving means disposed to receive said power stream;

means located adjacent said power nozzle in the boundary layer region of said power stream for causing changes in the specific volume of a portion of said fluid in the boundary layer of said power stream to cause said power stream to be proportioned to References Cited UNITED STATES PATENTS 2,916,873 12/1959 Walke'r 137 s1.s 3,001,539 9/1961 Hurvitz 13781.5 3,122,062 2/1964 Spivak 13781.5 3,137,464 6/1964 Horton 137-8l.5 3,168,897 2/1965 Adams 137-815 3,228,411 1/1966 Straub 13781.5

M. CARY NELSON, Primary Examiner 20 W. R. CLINE, Assistant Examiner 

